ISG15 and systemic lupus erythematosus: Interestingly, mRNA levels of OASL (median: 338.7, IQR 204.80–534.85 vs. 116.90, IQR 51.50–228.00, p < 0.001), MX1 (median: 1304.00, IQR 638.80–2679.50 vs. 375.70, IQR 214.10–1071.00, p < 0.001), OAS1 (median: 308.20, IQR 174.15–1027.10 vs. 168.00, IQR 94.10–335.30, p = 0.004), ISG15 (median: 0.51, IQR 0.32–0.64 vs. 0.13, IQR 0.07–0.30) and LY6E (median: 378.60, IQR 299.50–632.25 vs. 16.80, IQR 74.40–235.90, p < 0.001) in SLE patients with low C4 levels were significantly higher than in those who did not (Supplementary Table 3).